What Are Protists?
Right now you are familiar with three current models of classification:
1) A living thing is either a Prokaryote or Eukaryote.
2) A living thing is in one of the following kingdoms: Eubacteria,
Archaebacteria, Protista, Fungi, Plantae or Animalia.
We tend to overlay the two as follows:
Prokaryote = Eubacteria, Archaebacteria
Eukaryote = Protista, Fungi, Animalia and Plantae.
Eubacteria and Archaebacteria are designed from the same prokaryotic cell
composition. They are, however, different in many ways. First is the
environment in which they live, archaebacteria live in extreme environments
while eubacteria live in more habitable places. Another difference is their
cell wall composition, archaebacteria have a different protein/carbohydrate
matrix and will sometimes not even have a cell wall. Finally the other basic
difference is the physiological processes they have, the way their body
works is completely different. Archaebacteria cellular operations are more
similar to eukaryotic cells then eubacteria cells.
Q1. What are the names of the three domains?
A.
Q2. Why are the prokaryotes divided into two different domains in this
classification model? Be specific.
A.
Q3. What are two ways Archaea different from the Eubacteria?
A.
Q4. Which domain are the Protista in?
A.
Some biologists have married the three domain system and the five
kingdom system and come up with a six kingdom system (shown below).
Note:
Image from W.H. Freeman and Sinauer Associates, used by permission
Within this system, the Protists are the most difficult kingdom to classify!
It is certain that Protists belong in the domain Eukarya, but what
characterizes Protists? The Kingdom Protista has become a “dumping
ground” for organisms that don’t fit into the other three kingdoms. They are
always eukaryotes, but after that just about anything goes. Protist
classification is still in such flux that many of the group names are just not
worth learning. In fact, some biologists predict that it is likely the Protista
will be divided into 10-12 kingdoms in the coming years!
Q5. What are the general characteristics of Protista?
A.
Even though opinions vary widely, the Kingdom Protista is understood to
consist of three general groups: those that are animal-like, those that are
plant-like and those that are fungal-like.
We are going to focus our study around three interesting Protists. First, a
well-known representative of the Plant-like Protists:
Euglenoids
Euglena have flagella and a
gullet like an animal cell.
(heterotrophic injestion)
Euglena have chloroplasts like a
plant cell (autotrophic
photosynthesis)
And Euglena have been known to
lose their chloroplasts, forcing
them to absorb nutrients from
their envronment (Heterotrophic absorbtion and consumption)
www.emc.maricopa.edu/.../biobk/euglena.gif
Consequently, Euglenoids arguably can be classified as animal, plant and
fungus!
Q6. Two reasons the Euglenoids are considered to be animal-like are:
A.
Q7. What are three ways Euglenoids can eat?
A.
Q8. How do Euglenoids move? Do their flagella indicate the front end or the
back end of a euglena?
A.
Euglena wants to move towards the light for photosynthesis!
Q9. How might you design a simple little experiment to show that the
eyespot of Euglena helps it to find light?
A.
Euglenoids keep their shape because of an outer protein coat called a
pellicle. The pellicle provides protection and also helps prevent the cell from
osmotic bursting.
Q10. Define pellicle , and give its function.
A.
Q11. In all three of the organisms that you will be viewing you will
encounter contractile vacuoles. What is their purpose?
A.
Now, head back to the lab and….
View these on low, medium and high powers. Euglenoids are the
evolutionary king. Look for the following structures: Pellicle, contractile
vacuole, Flagella, Nucleus, Eyespot, Chloroplast. Follow the same
instructions as for the euglena above.
Field of view
Illustrate view HP
Now let’s move on to some animal-like protists; the Protozoa.
Ciliates
Ciliates are an example of animal-like
Protists. They are covered with up to
17,000 cilia beating from 40 to 60 times a
second in a coordinated fashion, used for
locomotion and to guide food into the gullet
to form food vacoles! There are contractile
vacuoles and anal pores to get rid of excess
water and waste products. As a result the
cell does not have a cell wall, which allows
the membrane to move and adjust. Trichocysts are filamentous proteins
that are usually found around or near the gullet. Believed to be used for
either catching prey, slowing predators or anchoring the cell while feeding.
Q12. What is the difference between a macro- and a micro- nucleus?
A.
Q13. How do ciliates deal with osmosis and the influx of excess water?
A.
Q14. How do ciliates eat and excrete wastes?
A.
Q15. What are trichocysts? What is their purpose?
A.
Now, head back to the lab and….
View these on low, medium and high powers. Paramecium was called the
“slipper animalcule”. Can you see why? Look for the following structures:
oral groove ( gullet), contractile vacuole, cilia, macronucleus, food vacuole,.
Follow the same instructions as for the euglena above.
Field of view
Illustrate view HP
Q16. How would the paramecium move about the slide?
A.
Q17. What are two roles for cilia?
A.
Q18. Does the paramecium change its shape like the amoeba? Why is
this?
A.
Rhizopods (Amoeba)
Another Protozoan group we shall examine is called Rhizopoda or Sarcodina.
A typical rhizopod is the ferocious predator Amoeba
proteus. The interesting thing about Amoeba is that
their cytoplasm can exist in two states: the liquid
“sol” endoplasm and the semi-solid “gel” ectoplasm.
The two consistencies work together to help the
Amoeba move and feed. When they extend their
cytoplasm it is called a pseudopod. The pseudopod is
used for locomotion as well as feeding. To feed they
extend two pseudopods around the food source and
enclose it in a food vacuole. When environmental conditions are harsh the
amoeba will create a cyst that encloses the DNA around a durable exterior
wall. When the conditions are favorable they will germinate into an
amoeba. When the amoeba germinates, some species will cause dysentery.
Which is diagnosed with the symptoms of abdominal pain, weight loss,
indigestion, diarrhea, blood in stool, chills.
Q19. So how do they move?
A.
Q20. What is a pseudo pod?
A.
Q21. How does an Amoeba survive harsh environmental conditions?
A.
The Amoeba seems like a harmless little guy, but some species are
downright nasty!
Q22. What are the symptoms of amoebic dysentery?
A.
Now, head back to the lab and….
From the culture provided. Look for the following structures: nucleus,
pseudopod, food vacuole, contractile vacuole, cell membrane. You know
the drill!!!
Field of view
Illustrate view HP
And finally….. summarize the similarities and differences in structure and
mode of living of the three organisms that you have studied… BE
ORGANIZED AND NEAT!!!